1. Field of the Invention
The present invention relates to hinges for pivotably connecting axially adjacent upstream and downstream wall sections of a gas turbine engine exhaust nozzle, and particularly to a nozzle hinge having a novel configuration for transferring cooling air from the upstream wall section to the downstream wall section.
2. Description of the Related Art
Maneuverability of modern high performance aircraft is greatly enhanced by extending the role of the engine exhaust nozzle beyond its conventional jet accelerating function. An exhaust nozzle with jet deflection capability can produce more rapid aircraft maneuvers at lower flight speeds than can be achieved by conventional control surfaces. In addition, reverse thrust capability incorporated within the exhaust nozzle can enable the aircraft to decelerate very rapidly for in-flight maneuvering purposes, and also to decelerate on landing to reduce the landing roll for short field operation.
Exhaust nozzles capable of such additional functions are known as multi-function exhaust nozzles. A typical such exhaust nozzle 10 is illustrated in FIG. 1. Nozzle 10 is a two dimensional exhaust nozzle having wall sections comprised of side walls 12, upstream converging flaps 14, and downstream diverging flaps 16 and 16a disposed between side walls 12. Such two-dimensional nozzles are preferred for multi-function applications since, unlike round section, axisymmetric nozzles, flaps 16 and 16a may be actuated differentially to thereby deflect the stream of hot combustion gases exiting through the nozzle for rapid pitch maneuvering of the aircraft. Such differential actuation of flaps 16 and 16a is illustrated in FIG. 3. FIG. 2 illustrates the position of flaps 16 and 16a for normal thrust operation. FIG. 3 illustrates the deflected positions of flaps 16 and 16a for rapid pitch maneuvering of the aircraft. FIG. 4 illustrates a closed position of flaps 14, 16, and 16a wherein the hot combustion gases are discharged through auxiliary exhaust nozzles 18 to produce a reverse thrust.
Since the wall sections of the exhaust nozzles are exposed to extremely high temperatures from the stream of hot products of combustion exhausting through nozzle 10, it is preferable to cool the interior surfaces of the wall sections to extend the service life of the nozzle and reduce maintenance requirements. Typically, prior art nozzles utilized a surface cooling configuration for the wall sections of the nozzles as illustrated in FIG. 5. FIG. 5 schematically illustrates a portion of exhaust nozzle 10 including a casing section 20 positioned upstream of converging flap 14 in the hot gas flow path. Casing 20 includes a liner 22 spaced from the interior surface thereof. Cooling air, typically bypass air from the turbine engine, is injected into cooling air flow passage 24 between casing section 20 and liner 22. The cooling air is ejected from cooling air flow passage 24 along the interior surfaces of flaps 14 and 16 to provide a film of cooling air on the interior surfaces of those flaps as illustrated by the arrows in FIG. 5.
However, the FIG. 5 configuration has significant drawbacks. First, the cooling air exiting from cooling air flow passage 24 is depleted as it flows along the surfaces of flaps 14, 16, and 16a by mixing with hot gases in the exhaust gas flow path. This depletion of the cooling air results in an excessive amount of cooling air flow being required to cool the flap sections 14, 16 and 16a. Excessive cooling air flow results in performance loss since the cooling air flow is typically taken from the turbine engine bypass air. Moreover, and with reference to FIG. 6, when flaps 14, 16, and 16a are deflected for pitch maneuvering of the aircraft, a severe angle exists at the junction of the convergent flaps 14 and divergent flaps 16 and 16a resulting in local flow separation 28 downstream of throat 30. Interior surfaces of flaps 16 and 16a, which depend on the conventional film of cooling air injected upstream of the flap for cooling, overheat since the turbulence in separated flow region 28 mixes the film of cooling air with hot gas flowing through the exhaust nozzle and thereby seriously diminishes the effectiveness of this type of cooling configuration.
Although the problem of cooling nozzle wall sections is equally applicable to axisymmetric nozzles as to multi-function, two-dimensional type exhaust nozzles, problems associated with cooling the rearmost, divergent nozzle flap on a multi-function two-dimensional type exhaust nozzle are magnified for two basic reasons. First, divergent flaps on two-dimensional type nozzles are longer for a given nozzle size and flow area than axisymmetric nozzle flaps and, thus, are more difficult to cool by the conventional method of injecting a film of cooling air at the flap hinge. The flaps of two-dimensional exhaust nozzles are longer than axisymmetric nozzle flaps since the side walls of the two-dimensional nozzle are fixed and the flap motion must therefore provide all of the required nozzle area variation. Two-dimensional nozzle flaps, the tips of which travel through a greater excursion to provide the required area variation, must necessarily be longer so that nozzle flap external contour angles are low as required for low drag and thus high performance of the aircraft.
Secondly, and in conjunction with the reasons noted above, during operation of a two-dimensional type exhaust nozzle with full jet deflection, a severe angle exists at the junction of the convergent and divergent flaps resulting in local flow separation downstream of the throat as described above with reference to FIG. 6.
In practice, two-dimensional exhaust nozzle flaps cooled by a film of cooling air injected at the hinge are subjected to excessive and nonuniform temperatures due to the general inefficiency of this type of film injected cooling flow. Such inefficiency has resulted in distortion, thermal fatigue, and cracking of the flap surface on some exhaust nozzles currently in operational service. Furthermore, as overall engine efficiency is increased in response to the ever present demand for improving fuel economy and range of the aircraft, the availability of bypass air for cooling the exhaust nozzle flaps is becoming increasingly scarce. To provide adequate temperature control of nozzle flaps on modern engines, a more efficient convection cooling means is required which, in general, can provide for more uniform distribution of cooling air over the wall sections of the nozzle.
Therefore, it is an object of the present invention to provide a hinge for pivotably connecting upstream and downstream exhaust nozzle wall sections wherein cooling air may be more efficiently transferred from the upstream to the downstream wall sections of the nozzle.
It is a further object of the present invention to provide a hinge connection for adjacent upstream and downstream wall sections of an exhaust nozzle which accommodates the use of liners disposed on the interior surfaces of the wall sections of the nozzle to define cooling air flow passages therebetween.
It is still a further object of the present invention to provide a hinge for adjacent upstream and downstream wall sections of a nozzle which is capable of more efficiently transferring cooling air along the upstream and downstream interior surfaces of the nozzle wall sections to thereby reduce the demand for cooling air flow resulting in increased performance and efficiency of the aircraft prime mover.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.